1. Field of the Invention
The present invention relates to photovoltaics (i.e. technology and research related to the application of photovoltaic cells in producing electricity for practical use) and, more particularly, to devices, systems and methods for generating alternating current electricity from photovoltaic cells.
2. Background Information
The demand and need for clean and renewable energy is becoming more urgent as earth undergoes global climate changes. Generation of electricity from coal produces over 50% of the carbon dioxide released into the atmosphere each year. Coal and other fossil fuels will also eventually run out. The hydroelectric power generation of electricity is limited to places where there is an adequate water source. Nuclear energy for the creation of electricity has the drawback of creating nuclear waste. However, one type of clean renewable energy is solar energy or sunlight. Solar energy is a constant source of clean energy that can shine on all areas of the surface of the planet.
Solar energy or sunlight can be converted into electricity by a photovoltaic cell. A photovoltaic cell known as a solar cell captures and converts sunlight into electricity. A solar cell is made from a semi-conducting material (a semiconductor) such as silicon that absorbs the sunlight which generates a flow of electricity through the solar cell. Because of the properties of semiconductors, positive and negative terminals of the solar cell are static and electron flow from a solar cell is uni-directional (i.e. the electricity can only flow in one direction). Thus, as with all photovoltaic cells, the solar cell produces only direct current (d/c) electricity. The problem with direct current electricity is that direct current electricity is difficult to transmit any appreciable distance, which limits its use. Thus, alternating current electricity is more usable than direct current electricity. Moreover, most electrical devices utilize alternating current (a/c) electricity.
Various prior art devices have attempted to provide suitable alternating current electricity from photovoltaic or solar cells. For instance, U.S. Pat. No. 4,075,034 issued to Butler on Feb. 21, 1978 (hereinafter, “Butler”) provides a solar converter for producing variable amplitude alternating current waveforms directly from solar energy by using a photo-voltaic cell bank array formed of a plurality of weighted photo-voltaic segments. A multi-sided high speed, rotating and light concentrating concave mirror system provides light on and past the weighted segments of the photo-voltaic bank to produce instantaneous output which are proportional to the number of cells scanned in each segment. A simulated alternating current (a/c) waveform is produced by suitable arrangement of the photo-voltaic segments. The simulated a/c waveform of Butler and its fragile manner (glass mirrors) of producing the simulated a/c waveform by the high speed rotating mirror is not efficient. Moreover, Butler is not easily scalable to produce larger voltages/amperes nor is it relatively maintenance free.
In U.S. Patent Publication No. 2005/0034750 by Rabinowitz published Feb. 17, 2005 (hereinafter, “Rabinowitz”), a solar cell alternating current generator is provided that uses a dynamic spinning ensemble of mini-mirrors to both concentrate and modulate rays from the sun onto a photovoltaic collector array. The focusing and superimposed spinning action produces single phase and multiphase alternating current electricity. The problem with Rabinowitz is again, the use of glass mirrors, the need for focusing the mini-mirrors and maintain their high speed spinning is not efficient.
In U.S. Pat. No. 6,774,299 issued to Ford on Aug. 10, 2004 (hereinafter, “Ford”), a solar alternating current electricity generator is provided that utilizes a rotating, partitioned array of photovoltaic cells. Contact brushes and wiring are provided to transfer the electric current to an applied load. The drawback to Ford is the need for contact brushes and wiring to generate the alternating current electricity. Moreover, the rotating photovoltaic cell vanes of Ford are not efficient.
In U.S. Pat. No. 4,728,878 issued to Anthony on Mar. 1, 1988 (hereinafter, “Anthony”), a solar energy electric generating system is provided for space vehicles which directly generates alternating current from ambient light without power conversion. Light incident to photocell arrays is mechanically or electrically gated to produce fluctuating direct current (d/c) electricity. A number of transforming devices are provided to convert the fluctuating d/c current to alternating current (a/c). Through variation of the frequency and duty cycle of the pulsing output voltage, frequency and phase relative to a reference may be controlled. However, with the Anthony solar energy electric generating system, the mechanical gating provides a square wave that is then conditioned to provide an alternating current waveform.
Last, in U.S. Pat. No. 4,577,052 issued to Schutten et al. on Mar. 18, 1986 (hereinafter, “Schutten”), an alternating current solar cell is provided by connecting solar cells (P/N junctions) in anti-parallel between a pair of main terminals. Light is provided alternately on the P/N junctions through a mirror system that splits the beam and causes the split beam to impinge on the P/N junctions.
It is clear from the above that the prior art devices for generating alternating current electricity directly from photovoltaic or solar cells are complicated, difficult to align and maintain, and cannot provide adequate scaling for small and large a/c current production.
In view of the above, it is desirable to have a solar powered alternating current (a/c) electricity generator, system and method that produces single or multi-phase a/c electricity that is simple, efficient and easily scalable in voltage and/or amperage.